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Requirements for Automotive AVB System Profiles

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Requirements for Automotive AVB System Profiles White Paper Contributed to AVnu Alliance TM Requirements for Automotive AVB System Profiles 3/15/2011 Author Junichi Takeuchi, Renesas Contributor Hideki Goto, Shinichi Iiyama, Takumi Nomura, Toyota Hajime Kosugi, NEC Engineering Michael Johas Teener, Yong Kim, Broadcom Contents herein are not necessarily endorsed by AVnu Alliance, and solely represent respective authors or companies’ views. Page| 1 Executive Summary The IEEE 802.1 Audio/Video Bridging (AVB) standards will enable time-synchronized low latency streaming services through 802 networks, ensuring interoperability between devices using the AVB specifications through a system profile called 802.1BA. Automotive applications, such as infotainment and drivers assistance, can deploy those specifications for an in-vehicle high bandwidth, synchronized network, as discussed in AVnu White Paper, AVB for Automotive Use, July 20, 2009. This paper presents automotive system profiles for general streaming applications as well as critical control applications, discussing basic profiles, additional network management, acknowledge and retry, and a low latency method. Figure 1. Automotive system profiles and IEEE802.1 AVB Page| 2 Assumptions The automotive system profiles in this paper are discussed under the following assumptions and goals. 1. The AVB network supports both automotive multimedia applications and critical control applications. 2. Critical control applications send and receive messages which require fault-tolerant, low-latency communication. 3. There will be no more than 32 endpoints in an automotive network. 4. There will be no more than 7 switch hops in any path taken by reserved streams. 5. The maximum cable length is 24m. The maximum total aggregate end-to-end cable length in a network is 30m. 6. The most time-sensitive applications use Class A streaming, which has a 125μs class measurement interval. Class B, which has a 250μs class measurement interval, also can be used for lower priority streaming. There are best effort frames using the lowest priority. 7. Maximum end-to-end delay for Class A streaming needs to be less than 100us for the cases where it is used for critical control applications (AVB guarantees 2ms for Class A, as default). 8. Maximum network recovery time needs to be less than 100ms, for the cases where it is used for critical control applications. Recovery time is measured from the detection of a failure event to the time that the network is ready to transmit data from applications. Page| 3 Contents 1. Basic network requirements and profiles 1-1. Standards: 802.1AS, Qat, Qav, BA, and 1722, 1722.1 1-2. Setup and Operational procedures ・ Grand Master selection ・ System management with 1722.1 1-3. General Security procedure ・ Ethernet LAN Security Requirements (trusted network) 1-4. Network application: Multimedia example ・ Audio and Video Lip-Sync 2. Additional requirements for Critical control and Converged backbone network 2-1. Fail-safe systems and Quick recovery ・ RSTP with quick recovery ・ RSTP Root selection ・ End-point failure discovery 2-2. Acknowledge and Retry 2-3. AVB automotive Frame definition ・ Acknowledge and Retry, and CAN 2-4. Smaller Frame size for low latency 2-5. Requirements for ultra-low latency Appendix A. General Security procedure methods and examples ・ In-Vehicle LAN Security Considerations and Use Cases Appendix B. Audio and Video Lip-Sync example Page| 4 1. Basics network requirements and profiles 1-1. Standards: 802.1AS, Qat, Qav, BA, and 1722, 1722.1 Automotive Ethernet AVB products comply with the base standards in Table 1, although some products might not use all these specifications, selecting some subsets based on the requirements of the target system. On the other hand, some products might add additional specifications discussed in this paper for converged network systems, or critical control systems. Table 1. Standards for automotive Ethernet AVB Abbreviation name comments 802.1AS Timing and Synchronization for Time-Sensitive - Specified by The Audio/Video Applications in Bridged Local Area Networks Bridging Task Group 802.1Qat Stream Reservation Protocol - All approved IEEE Standards 802.1Qav Forwarding and Queuing Enhancements for Time-Sensitive Streams 802.1BA Audio Video Bridging (AVB) Systems - System profiles that are common to any application - In progress 1722 Layer 2 Transport Protocol for Time Sensitive - Stream packet format Applications in a Bridged Local Area Network - Approved IEEE Standard 1722.1 Device Discovery, Enumeration, Connection - In progress Management & Control Protocol for 1722 based devices 1-2. Setup and Operational procedures While one of the advantages of Ethernet is a simple configuration, which enables data transmissions without complicated network settings, there are a few parameters that must be set either by users during initialization procedures (if the network configuration can be altered) or by the manufacturers (if the network configuration is semi-static or fixed). Another advantage is Plug-and-Play, but the system doesn’t necessarily have to use the dynamic configuration default, because automotive network is a provisioned network, and electronic control units (ECU) in an end-point usually have pre-determined functions. The network could operate using default settings, and could optimize some of the settings during system initialization. Page| 5 Grand Master selection The best master clock algorithm in 802.1AS determines the grand master and constructs a time-synchronization spanning tree with the grandmaster as root. In this process, time-aware systems send best master selection information to each other by using Announce messages, which contains a priority vector with some attributes specified in 802.1AS. Developers should provide electronic units with appropriate attributes such as system type priority, clock class, clock accuracy, or time source of the system, referring to 802.1AS standard. For example, central gateway unit is usually the first one to startup among ECUs in the entire in-vehicle network, and also last one to shutdown. It tends to be the first priority and highest quality unit. There is another higher priority unit, yet less than central gateway unit, and it is head unit including GPS, which is a main source of information for drivers. Then, the central gateway should have the highest priority value used for the grand master selection process, and the head unit should have the second highest value. System management with 1722.1 The protocols in 1722.1 are complementary to other AVB standards and profiles, since 1722.1 specifies an application-level connection procedure for the AVB network system. It includes 1) Service Discovery process, in which a 1722.1 controller identifies other 1722.1-capable nodes, 2) Enumeration process to find capabilities of the nodes, 3) Connection Management to connect and disconnect virtual links between media sources and media sinks, and 4) Control protocol. The first three functions can be bypassed for pre-configured networks where the configuration will not change, such as in a typical automotive application. The control protocol is very simple, yet easily extended to support industry-specific command sets such as those needed for automotive control and sensing applications. IEEE 1722.1, although requiring only simple layer 2 protocols (not using TCP/IP), is also designed to be optionally carried on TCP/IP networks using familiar HTTP protocols. 1722.1 suggests that all “controller” devices be capable of performing a simple IP proxy function so that pure IP-only devices on the network can still participate in device discovery, enumeration, and control. Page| 6 1-3. General Security procedure Ethernet LAN Security Requirements (trusted network) Ethernet technology is well-known in the industry, and securing the network from hacking and un-authorized access is required. The best security practices from the IT industry are adoptable to in-vehicle network with the same effectiveness. The general concept is to protect the network infrastructure and control access at the edge (i.e. the first switch connection from the end-point). The cost-benefit balance will be maintained by protecting the network access for various use cases. End-point Access Instrument Controlled. Panel Body Central Ctrl ECU Head Unit Camera Gateway Switch to Switch E connections are Switch E Switch trusted. GE E 10GE E E E E E Switch to Switch 1 Gb/s connections are Switch . trusted. 100 Mb/s E E E E E 100 Mb/s . LCD End-point Multi- Display Access Camera channel RSE Controlled. Audio Amp Ethernet Network in IT Ethernet Network in Automotive Figure 2. Ethernet network comparison (trusted network) Many features are available within IEEE 802.1Q Bridge implementations to provide LAN access security methods, and some of these are described in Appendix A. 1-4. Network application: Multimedia example By selecting some of the AVB standards described in the previous sections, a high-speed automotive network can be implemented. Here, we discuss application-related functions rather than network functions, in order to show how an automotive network can benefit from 802.1 AS and 1722. Page| 7 Audio and Video Lip-Sync One of the key advantages of Ethernet AVB is providing all media synchronization in its native form, with a transport protocol that provides presentation time to the application layer such that real-time synchronized rendering, i.e. “lip-sync” can be achieved. Because AVB provides the network time accurate to 1μ sec anywhere in a network, presentation time carried in a transport protocol can be honored by all media renderers in a network. A detailed example of this use of presentation time in AVB network is in Appendix B. Summary There are multitude of network-enabled in-vehicle Ethernet use that can be serviced with IEEE 802.1, IEEE 802.3, and IEEE 1722 standards that provide professional quality streaming, precision time synchronization in Ethernet, and related transport protocols. The use cases include vehicular multi-media, driver-assist camera and displays, and consumer owned portable content integration. There are a few further requirements that helps to harden the use of Ethernet AVB to meet the all of the vehicular backbone requirements.
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